Composites comprised of aligned carbon fibers in chain-aligned polymer binder

Abstract

A method for enhancing internal layer-layer thermal interface performance and a chip stack of semiconductor chips using the method. The chip stack includes a first chip with circuitry on a first side, a second chip coupled to the first chip by a grid of connectors, and a thermal interface material pad between the chips. The thermal interface includes nanofibers and a polymer that allows for optimal alignment of the nanofibers and polymer chains.

1 . A chip stack of semiconductor chips with enhanced cooling comprising:
 a first chip with circuitry on a first side;   a second chip electrically and mechanically coupled to the first chip by a grid of connectors;   a thermal interface material pad between the first chip and the second chip, wherein the thermal interface material pad further comprises:
 a plurality of nanofibers within a matrix with aligned polymer chains, both of which are aligned parallel to mating surfaces of the first chip and the second chip; and 
 at least one thermosetting polymer that will un-crosslink and reduce viscosity of the thermal interface material to allow for extruding the thermal interface material through a die to orient the conductive axis of the nanofibers and the polymer chains in the desired direction. 
   
     
     
         2 . The chip stack of  claim 1 , wherein the un-crosslinking is by heating the thermal interface material to at least 110° C., and the re-crosslinking is by cooling the thermal interface material to approximately a range of 23° C. to 75° C. 
     
     
         3 . The chip stack of  claim 1 , wherein the un-crosslinking is by adding a solvent to the thermal interface material, and the re-crosslinking is accomplished by evaporating off the solvent in the thermal interface material. 
     
     
         4 . The chip stack of  claim 1 , wherein the plurality of nanofibers in the thermal interface material pad are arranged so that both ends of each of the plurality of nanofibers are perpendicular to an edge of the thermal interface material pad closest to each of the plurality of nanofibers. 
     
     
         5 . The chip stack of  claim 4 , further comprising:
 a heat sink attached to one surface of the first chip.   
     
     
         6 . The chip stack of  claim 4 , further comprising:
 a heat sink attached to one surface of the second chip.   
     
     
         7 . The chip stack of  claim 4 , further comprising:
 a heat sink attached to one surface of the first chip and attached to one surface of the second chip.